KR20040083442A - Method and device for optically measuring the surface shape and for the optical surface inspection of moving strips in rolling and processing instalations - Google Patents

Abstract

The present invention relates to a method and apparatus for optically measuring the surface shape and optically inspecting the moving elongated body, whereby surface shape measurement and surface inspection are integrated. The projector applies a line pattern to the object to be measured. The camera records the surface of the target being measured and compares the image information with the reference pattern. Two high resolution cameras additionally detect defects on the target being measured. This unique measuring technique is particularly suitable for the combined plane and surface measurement of metal strips in rolling equipment.

Description

FIELD OF THE INVENTION METHOD AND DEVICE FOR OPTICALLY MEASURING THE SURFACE SHAPE AND FOR THE OPTICAL SURFACE INSPECTION OF MOVING STRIPS IN ROLLING AND PROCESSING INSTALATIONS}

Contact measurements commonly used in cold strip mills are only possible in hot strip fields at significant expense to maintain due to the high strip temperature of about 1000 ° C.

Strip flatness is measured for it, preferably without contacting hot rolling mills. For example, it is known to measure the meridian from the flatness by the light spots projected onto the strip. The position in space of the light spot generated on the surface of the strip is detected using a range finder, preferably by means of a laser beam.

The two planar position common-vertical coordinates of a particular point on the surface can be known from the position of the scanning or irradiation beam relative to the surface of the strip. The height common-vertical coordinate of the point on the surface currently being measured is detected by the position sensor. The position of the image point on the sensor changes simultaneously with the height common-vertical coordinate.

Using multiple radiation sources and sensors, a flat image can be made over the entire width of the strip made from the measurement results of the light spots projected onto the strip at a particular distance away. Nevertheless, in this method the areas between the points of light are not detected and the flatness is not determined if the continuous strip forms strip-shaped measuring gaps. This can also result in measurement errors, for example through fluttering of the strip which is detected by a measuring method such as unevenness of the strip.

It is known in the automotive industry to measure relatively small surfaces using the Moire technique. In this method, the interference pattern is generated on the surface of the object by the light source. The interference pattern is detected using a charge-coupled device (CCD). The cameras are aligned to form an angle between the light source, the surface and the camera. Using a reference grid in the image plane, the so-called moiré effect is obtained by superposition of the detected pattern and the reference pattern. The height difference can be determined quantitatively from the moire line.

The moiré technique provides more accurate measurement results than the measurement using light spots, which in addition substantially covers the entire surface to be measured and avoids the aforementioned measurement gaps. However, its use involves problems in particular in hot rolling mills.

In order to determine the height difference of the rolled strip, a complicated transition of the pattern detected by the camera is required. The height difference depicted as moiré lines cannot be converted into quantitative measurements in real time.

Since it is hardly possible to use a measurement for direct adjustment of rolling parameters to improve the flatness of a continuous strip, a fast result in a rolling mill train is exactly what is required from the measurements. In addition, good interference patterns for industrial applications lack contrast and strength.

From US 5,488,478 an apparatus for measuring the surface of a metal strip is known, using a laser beam that generates lines on the metal surface, which is recorded by several line scan-cameras and compared with reference patterns surface geometry It is analyzed to determine the geometry. This device requires considerable structural effort and, in addition, only allows schematic and partial information about the surface geometry of the strip.

From DE 197 98 922 B1 it is known how a line pattern is generated on a measurement surface, the line pattern is detected by a camera capable of resolving it, and the measurement data obtained is compared with a reference measurement. The measurement results by the process control computer are directly converted into control parameters for the finishing train and coordinated with each other. Since an insensitive slide projector is used rather than sensing laser optics, this method has the advantage of high sensitivity to disturbance, which is particularly important in rolling mills.

The surface of the strip of rolling stock that has moved or stopped will be understood by measuring the surface.

The present invention relates to a method and apparatus for optically measuring surface shape in rolling and processing equipment and for optical surface inspection of moving strips.

Figure 1 shows calculating and detecting the measuring lines in the length of the strip.

2 shows a projector and a camera aligned behind a finishing train

3 shows a projector and a camera arranged in front of a coiler pit.

4 is a block diagram of a flatness control system.

5 and 6 show the integration of flatness measurement and surface inspection in one device.

The projector with the slide creates a line pattern on the strip surface. For this purpose the projector is mounted above the metal strip and projects a line pattern on the surface of the metal strip, so that the lines preferably run across the strip surface and thus record the full width of the strip.

For example, a CCD camera with a resolution of 8 pixels per line detects lines traveling across the strip surface. If the strip is completely flat, a uniform pattern of straight lines with constant line spacing is formed.

The bending of the strip surface from the ideal plane results in a change in spacing between the lines in the uneven area. This change is recorded by the camera. It can be calculated in a simple way compared to the ideal pattern and converted into height differences.

This system allows for quick determination of the actual height difference of the strip surface and in this way enables the measurement of the continuous length of the strip in real time. This has the advantage that the measurement results result in the rolling parameters to be fitted immediately after the non-flatness appears.

This allows measurements that are not affected by spurious measurement results. Such erroneous results are obtained using existing measuring systems, for example as a result of the movement of the entire strip surface in relation to the height common-vertical coordinates (fluttering). The invention also allows for transverse arching of the strip to be determined. Existing measurement systems only measure the length of the strip fibers. In addition, the strength and thickness of the measuring lines can be adapted to meet different conditions. Problems of fine low-intensity and low-contrast moiré lines do not occur.

The system of the invention is particularly suitable for measuring on strips coming from a finishing stand combined with the measurement of strips on a coiler. By this arrangement variation in the flatness of the strip due to strip cooling between the finishing stand and the coiler, the flatness control can be detected and evaluated.

The measurement data can be evaluated for the control of the finishing stand and coiler and the control of the coiling line.

Measurement results incorporating deviations from the intended values make it possible to immediately and interdependently adapt the parameters relating to the finishing stand, cooling line and coiler.

In addition to using it for measuring flatness in the finishing train, the system according to the invention can be used in subsequent production lines, such as in the control of stretch straightening devices and pickling lines. Can be used.

In addition to the flatness, the numerical stability of geometric values, such as thickness, transverse thickness profile and width, as well as surface conditions detected by the surface inspection system, is due to the relative quality characteristics of rolling and stripping and further processing of the sheet. Part. It is desirable to maintain tight tolerances, and especially with the ever-increasing automation of production processes, it is also important to measure the quality of the finished product and to measure the pretreatment process as free of disturbances as possible.

Therefore, the on-line acquisition of the above-described quality characteristics in the treatment process and process optimization through control and closed loop control belongs to an important role in quality improvement.

For the determination by the measuring technique of the above-mentioned features, the optical system (flatness measuring system), strip width (width measuring system) and surface condition (surface inspection system) and strip thickness for determining flatness or strip thickness "One-purpose-devices" such as radioactive systems for determining a profile that intersect are known in the art. These systems operate independently of each other and require significant structural space, and are spaced apart from each other in order to exclude interference from each other.

The prior art is preferably used for surface inspection optical systems. These typically include the following components:

Illumination units for illuminating strip surfaces, camera units for recording strip surfaces without gaps, processing units for processing camera image information, and interface units for processing classification results and displays.

In general, the system type of strip surface inspection is divided into a system with line cameras and a system with several CCD-matrix-cameras.

The illumination should preferably be designed in such a way that errors that can occur in a particular production line can be detected with the best optical contrast as possible. In general, matrix-camera stroboscopic illumination is used to deliver the required amount of light at short time intervals. As line camera permanent illumination units are generally used, motion blur is suppressed by the electronic camera shutter.

Attempts have been made to achieve high homogeneity of illumination since image quality and detection performance are directly affected by it. Each heterogeneity in illumination must be adapted by amplifying the image signal. This in turn results in a reduction in signal-noise-separation. The use of matrix-cameras favors the homogeneity of the illumination, since the correction through image amplification in both directions is much more extensive than through a single line, like a line-camera. All illuminations are performed in the visible and infrared or ultraviolet in the spectrum. Light emission may be divergent or focused through suitable optical components.

The camera technique is preferably dimensioned in such a way that the minimum error magnitude can be resolved under all speed conditions of the strip. Image recording takes place in relation to the strip length. In order to make full use of the dynamic-spectrum of the camera, the image brightness is preferably controlled automatically.

For systems that have been in full use for some time, a clear overbalance is registered about "line-cameras," where line-camera systems were able to preempt the market and were initially placed on surfaces with low requirements that were fairly simple to inspect. Because it was used. Many systems using matrix-cameras have only been established in the last two or three years, and not just for that reason in running-in phases or performance checks. At present, it can be said that there is in principle no significant difference in performance between the matrix and line camera systems. However, line camera systems are less in scope in terms of setup and operation.

Camera resolution is determined by the smallest error magnitude that can be classified and is limited by optical imaging laws. In order to obtain a good grade in the downstream process, the minimum error magnitude can be covered by at least 16 detected pixels, which are preferably pixels detected as defects by the system. For optimization of certain error imaging, the choice of viewing direction and the tilt of the camera are important. Bright field and dark field observations are prominent, and recently, side-field observations have also been used.

By combining separate lights and camera arrangements, the optimum installation conditions for each application can be improved.

In the image processing unit, the continuously recorded surface image is checked with respect to the information item. The properties of the "error image" can be compared with the logged error properties. In each case, automatic classification may be enabled in one of the "pre-trained" error classes. Extraction and comparison of image features currently requires great computational power.

Current inspection systems compare recorded image points with threshold levels. The image point identified as the defect is set, everything else is not set. From these "binary images" and using the luminance information logged for each image point, parameters for classification are obtained.

In order to provide timely critical strip information and control information to the surface inspection system, the interface unit is typically designed for a specific application. This is the standard task with regard to automation and database technology.

In the prior art, a system for flatness measurement and a system for surface inspection are described, which are spaced apart from each other and operate independently of each other, in order to exclude interference from each other, which requires considerable structural space.

It is an object of the present invention to provide a system which allows for improved measurement and which can be further designed to save space.

At the end, an apparatus and method according to the independent claim is presented.

Through the possibility of integrating the device and the method, a synergy effect of increasing measurement reliability is obtained.

The present invention is preferably based on integrating flatness measurement and surface inspection based on image recognition using a fast line-camera with high resolution. The system can additionally be used to determine strip-width or sheet-width.

By way of example, the following advantages can be addressed:

The number of components required is reduced through "multiple uses", in particular with respect to lighting units.

The installation space required is significantly reduced compared to single use systems.

Including the results from the surface shape measurement into the width measurement increases the measurement reliability of the width measurement in the case of uneven strip shapes. Incorporating the results from surface profile measurements into the surface inspection is especially distortion-free error indication for strips that are not pass-line or do not have a flat strip shape due to flattering. enable representation. Thus, in sections where the strip is not tightened by an additional device such as a deflection roller, image recording by line cameras is possible. Integrating the results of surface-shape analysis capabilities significantly reduces the pseudo-error portion of the surface inspection. The invention will be explained in more detail by the embodiments with reference to the embodiments depicted in the drawings.

The method according to the invention for optical measurement of surface shape and optical surface inspection can be used for moving or stationary elongated bodies, preferably for strips or sheets.

The apparatus according to the invention preferably has a structure according to Fig. 5, wherein the line cameras are located coaxial with the projector. Measurement lines 2 across the strip 1 are produced on the measurement or strip surface 4 using the projector 3.

The measuring arrangement is arranged in one case exiting from the finishing stand 6 on the instrument case 13 and the other case in front of the coiler 7. The CCD camera 5 is located on the side of the machine case close to the coiler 7 in the water cooling ising. The projector 3 is located on the side of the machine case away from the coiler 7. The hydration is cooled with air to remove heat. Cooling of the projector 3 and the camera 5 is necessary to remove their inherent heat and radiant heat from the strip 1, which is about 1000 ° C.

The camera 5 and the projector 3 are arranged in succession with respect to the direction of movement of the strip and aimed at the strip area located between them, where a fine pattern is calculated and sampled. The projector used may be, for example, a xenon light source, which yields a line pattern that is easily readable even in hot slabs.

The unevenness of the strip surface 4 causes the measuring lines 2 to follow an irregular course or deviate from the geometric straight line.

Thus, by the CCD camera 5 in the measurement lines 2, changes in the course caused by non-flatness are also detected. After it is detected, the measured image is compared with a reference pattern previously recorded with a computer. Parameters for control of the height difference and the finishing train are derived directly from the deviation.

A complete picture of the flatness of the strip or sheet 1 is obtained by it as it moves along the direction of the arrow. In principle, measurements can also take place with stationary rolling stock.

From the drawing of the flatness control system (Fig. 4) we can see the design according to the invention. The hot strip 1 passes through the finishing rolls 6 and the strip cooling line 8 to the coiler 7 of the coiler pit. On running out of the finishing rolls 6, the flatness of the hot strip is detected, analyzed and evaluated for control of the last stand of the finishing rolls (roll bending and tilting). This inner flatness-control loop 9 is supplemented by an outer flatness-control loop 10. By measuring the strip flatness before the coiler 7 after the strip cooling line 8, the outer flatness-control loop 10 is designed to suit the intended value of the inner control loop.

Using the measured values detected behind the strip cooling line, the intended values for the first secondary control loop 11 and the coil tension 7 are fitted to ensure that the intended values for the cooling line 8 are fitted. The second secondary control loop 12 is calculated.

Sampling of the strip surface to detect defects (errors) is achieved by additionally installed high resolution line cameras (Figure 5), which makes it possible to detect surfaces across the entire strip width. Two line cameras are aimed at the "bright" strip illuminated by the projector. The optical axis of the camera is oriented in the direction of the projection beams to record each irradiated strip through the line camera even when there is a change in the height of the strip surface. Due to the arrangement of the two line cameras taking into account the arrangement of the projector relative to the strip surface, one camera will operate in the "bright field" and the other camera will operate in the "dark field". 5, it is necessary to optimize detection performance for surface defects of different characteristics.

For geometric deskewing of the image of the line cameras, height profiles along the measuring fields obtained by the flatness measuring system can be used.

In addition, it is also possible to directly link error images with information from flatness measurements, particularly elongation profiles across the longitudinal direction, e.g. due to local exceedance of breaking strength, during the rolling process. The identification of errors such as transverse cracks and edge cracks, which can be improved, can be improved, whereby the indication of the cause of the error can be reduced simultaneously.

In addition to surface inspection, image information of two line cameras can be used in combination with the results of parallel flatness measurements for quantitative determination of the height resolution of strip end position and strip width. This height profile and strip end information detected by the line cameras along the measurement field determined using the flatness measurement system can be used for geometric deformation.

Claims (10)

In the method for optical measurement of surface shape and optical surface inspection of elongated bodies, Wherein the method incorporates surface shape measurement and surface inspection. An illumination unit for measuring the surface of a strip or sheet, characterized in that it is used for measurement of surface shape and for surface irradiation. The method of claim 1, wherein the result of the surface shape measurement is included in a surface inspection. The method of claim 1, wherein the image is recorded by line cameras. 5. The method of claim 4, wherein the line cameras are located in one axis with the projector. 2. The surface strip according to claim 1, wherein the surface geometry is obtained by generating lines on the strip surface by means of a light source and a plurality of lines 2 are produced by projection, in particular by a projector. Generated in a phase. 2. The method according to claim 1, wherein a pattern (2) on the strip surface (1) is produced for flatness measurement. A method according to claim 1, characterized in that the pattern (2) is compared by the computer with the reference pattern after being detected by the camera. The method of claim 1 wherein the measured value is used for control of the finishing train. 2. Method according to claim 1, characterized in that xenon light is used as the projection light source (3).